Like all parts of the body, the brain is composed of living cells that require a blood supply to provide oxygen and nutrients. A hemorrhage in a blood vessel in the brain or in the space closely surrounding the brain is a common cause of strokes. Hemorrhage refers to bleeding into the brain, usually because of a problem with a blood vessel, for example, an aneurysm.
An aneurysm is an abnormal bulging and/or weakening of a blood vessel wall. The wall may smoothly bulge outwardly in all directions (a fusiform aneurysm) or it may form a sack arising from one wall (a saccular aneurysm). If the aneurysm ruptures, a hemorrhage occurs. This can compress and irritate the surrounding blood vessels, resulting in a reduced supply of oxygen and nutrients to the cells, possibly causing a stroke.
Aneurysms can be treated from outside the blood vessel using surgical techniques or from inside the blood vessel using endovascular techniques. Endovascular treatment of an aneurysm is performed using a catheter. X-ray, magnetic resonance imaging (MRI) equipment, or other visualization equipment may be used to view the progress during a procedure.
Electrolytically detachable embolic devices have been proposed to fill aneurysms. A core wire or catheter may be used to introduce an embolic coil into an aneurysm. The embolic coil may be attached to the distal end of the core wire by an electrolytic sacrificial joint. Once the embolic coil is located in the targeted aneurysm, the coil may be detached from the core wire and deployed in the aneurysm by running an electric current through the electrolytic sacrificial joint. Within a short period of time after the filling the aneurysm with the embolic coil, a thrombus may form in the aneurysm and, shortly thereafter, complemented with a collagenous material that significantly lessens the potential of the aneurysm rupturing.
The inventor of the present invention has recognized that embolic devices may utilize shape-memory polymers or metals, polymer-coated coils fused together by heat, or other thermo-sensitive materials for thermally controlled expansion of the embolic devices in aneurysms. Warm saline injections may be used to deliver localized heat to these devices, but this method of heat delivery may be difficult to reproduce in a controllable manner. Further impediments to this concept may include differential mixing of saline with blood due to dissimilar thermodynamics, non-uniform heat distribution, heat transfer out of the catheter, and/or physician compliance in maintaining reasonable saline temperature and injection rates.